As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate a large and variable number of communication devices transmitting a growing volume of data over wide cellular areas with fixed resources. Traditional communication system designs have become challenged to provide reliable communication over a reasonably wide geographical area in view of the general need to limit transmitter power and bandwidth for the rapidly growing customer base and expanding levels of service.
The Third Generation Partnership Project Long Term Evolution (“3GPP LTE”) project is the name generally used to describe an ongoing effort across the industry to improve the universal mobile telecommunications system (“UMTS”) for mobile communication to cope with continuing new requirements and the growing base of users. The goals of this broadly based project include improving communication efficiency, lowering costs, improving services, making use of new spectrum opportunities, and achieving better integration with other open standards. The 3GPP LTE project is not by itself a standard-generating effort, but will result in new recommendations for standards for the UMTS.
In wireless communication systems where control channel resources are limited, various techniques to optimize utilization of control channel resources have been considered. One optimization technique utilizes persistent or semi-persistent allocation of transmission resources assigned to user equipment. Semi-persistent allocation of transmission resources generally refers to initial transmissions that are persistently scheduled, and retransmissions (e.g., after a negative acknowledgment) that are dynamically scheduled. Uses of the terms “persistent” and “semi-persistent” resources in discussions of 3GPP communication systems generally refer to similar processes, and they will be used interchangeably herein. The optimization technique assigns semi-persistent resources for transmission in a downlink (“DL”) or in an uplink (“UL”). For example, in systems configured to support the 3GPP LTE project, semi-persistent and dynamic resource scheduling has generally been included in system designs.
For semi-persistent scheduling, a pattern of periodic transmission/reception resources are assigned to user equipment (“UE”) using higher layer signaling and physical downlink control channel (“PDCCH”) signaling. For example, for a resource with a 20 millisecond (“ms”) time periodicity, the periodicity is signaled with higher layer signaling (e.g., radio resource control (“RRC”) signaling), and is assigned using a PDCCH, allowing the user equipment to transmit or receive using pre-assigned resources without further explicit Layer 1/Layer 2 (“L1/L2”) control signaling (i.e., without further PDCCH signaling).
The user equipment generally maintains the value of a new data indicator (“NDI”) flag, which signals to the receiver the new or repeat nature of a transmission. Normally, with dynamic scheduling, the NDI flag is signaled explicitly in control signaling in a PDCCH. However, for semi-persistently allocated resource scheduling, PDCCH signaling and thus an NDI flag, is not transmitted for the initial transmission to conserve transmission resources. There is also the issue of how an NDI flag would be signaled or otherwise handled for retransmission of data that might be made, for example, by a base station in response to a “negative acknowledgment” (“NACK”) signal from user equipment to indicate failed data reception in a hybrid automatic retransmit request (“HARQ”) arrangement. The user equipment requires an NDI flag so that it can treat received data as a new input or as a repeated transmission of previously received data that should be combined therewith for its reliable interpretation. The NDI is also used for uplink transmissions. In an LTE uplink, the NDI is sent in a downlink on the PDCCH, and based thereon, the user equipment either retransmits or transmits new data.
Considering the limitations as described above, a system and method to reliably indicate a value for an NDI flag for semi-persistently allocated transmission resources for various signaling conditions or other allocation without the PDCCH is not presently available for the wireless applications that lie ahead. Accordingly, what is needed in the art is a communication system that can reliably exchange an NDI flag between a base station and user equipment for the various resource allocation arrangements and for the various signaling situations that can be anticipated to be encountered.